The present invention concerns a power supply apparatus for a shaping machine and a method of power supply for a shaping machine.
The term shaping machines can be used to denote injection moulding machines, injection presses, presses and the like.
It is known for the power to be provided for electrical axis motions by a supplier (=power provision) via a DC bus. That is effected by rectification of the mains input voltage and an additional increase thereof by 35% relative to the rectified value. That DC voltage is changed into a rotating field again in the power inverter in order to drive the motor therewith. The rotary speed and the power of the motor can be regulated by the configuration of that rotating field. In the case of regenerative-capable systems, it is also possible for the flow of energy to be reversed so that power stored in the mechanical system is fed back into the mains again in the same way.
The supply power is calculated firstly in relation to the nominal power demand and secondly the maximum total peak power in the system. For example, in the case of injection moulding machines in the high-performance field, it is striking in that respect that the ratio between peak and nominal power is up to 4:1.
As the power output stages must be designed for the maximum power to be involved that ratio requires the use of large output stages which are then not used to full capacity. That situation drives up the costs of the drive systems.
As the overload must be provided exclusively by the mains, then high peak power tariffs are implemented by the mains network operator.
To sum up, the following disadvantages occur in power supply apparatuses in accordance with the state of the art:
I. Large supply apparatuses
II. High losses
III. High costs
IV. Poor capacity utilization
V. High peak powers
VI. High reactive power demand.